Bar spring eyeglasses: a type of pince-nez.
Because of the discovery of astigmatism, a type of lens fixation was needed in eyeglass (pince-nez) frames to maintain a constant angle for the patient's astigmatism. Bar spring frames were an answer to this problem.
Rosenthal
J W
JW
D001251:Astigmatism / Q000266:history / Q000628:therapy; D004739:England; D004867:Equipment Design; D005139:Eyeglasses / Q000266:history*; D005858:Germany; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans